Surface acoustic wave device

ABSTRACT

A surface acoustic wave device includes a substrate, a plurality of terminals including at least an unbalanced terminal and balanced terminals, and at least one of surface acoustic wave element disposed between the unbalanced terminal and the two balanced terminals. Different signal lines connected to the same surface acoustic wave element intersect through insulating films.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a surface acoustic wave device, andmore particularly, to a surface acoustic wave device including a surfaceacoustic wave element.

2. Description of the Related Art

In a conventional balanced-type SAW (surface acoustic wave) filterhaving an unbalanced-to-balanced-type filter of a first stage and abalanced-to-balanced-type filter of a second stage that arecascade-connected, signal wirings for connecting the balanced terminalsof the filters are disposed between the stages and a ground padconnected to the other terminal of an unbalanced terminal IDT(interdigital transducer, comb-shaped electrode) of the first stage isdisposed between the signal wirings.

FIG. 5 is a top view of a substrate of a surface acoustic wave device ofa related example. The substrate 1210 is a LiTaO₃ single crystalsubstrate and, a metal film having a fixed pattern is provided on themain surface 1212, as shown in FIG. 5. That is, a balanced-type SAWfilter is provided, in which a longitudinally coupled resonator-typesurface acoustic wave filter 1220 of the first stage and alongitudinally coupled resonator-type surface acoustic wave filter 1230of the second stage are cascade-connected, a pad 1251 defines anunbalanced terminal, and pads 1252 and 1253 define balanced terminals.In an area enclosed by the filters 1220 and 1230 and wirings 1241 and1242 for cascade-connecting the filters 1220 and 1230, a ground pad 1256connected to an IDT 1223 including the unbalanced terminal 1251 isdisposed (see, for example, Japanese Unexamined Patent ApplicationPublication No. 2002-300004).

Furthermore, in recent years, there has been a requirement for having abalanced-to-unbalanced conversion function or a so-called balun functionincluded in a surface acoustic wave filter used in the RF stage of aportable telephone. Lately, in particular, a longitudinally coupledresonator-type surface acoustic wave filter which provides ahigh-frequency wave and also which provides a balanced-to-unbalancedconversion function has become more common as a bandpass filter of theRF stage of a portable telephone.

The surface acoustic wave filter having a balanced-to-unbalancedconversion function is connected to a mixer IC (hereinafter, referred toas a balanced-type mixer IC) having a balanced or differential input andoutput. When this balanced-type mixer IC is used, the effect of noise isreduced and the output is stabilized. Thus, this surface acoustic wavefilter is often used to improve the characteristics of portabletelephones.

A surface acoustic wave filter having a balanced-to-unbalancedconversion function may include various structures. Each of the variousstructures has benefits and detriments and may be properly used inaccordance with the intended uses and requirements. One known structureincludes balanced terminals that are connected to both terminals of oneIDT.

For example, in FIG. 6, an element chip 30 of such a surface acousticwave filter is schematically shown. The surface acoustic wave filter isconfigured to have a balanced-to-unbalanced conversion function suchthat both ends of the middle IDT 1 of a longitudinally coupledresonator-type surface acoustic wave filter element 6 including threeIDTs 1, 2, and 3 and two reflectors 4 and 5 are connected to balancedsignal terminals 11 and 12, respectively, and such that one end of eachof the left and right IDTs 2 and 3 is connected to an unbalanced signalterminal 13 through an IDT 7 of a surface acoustic wave resonator 10 inwhich reflectors 8 and 9 are disposed on either side of the IDT 7. Inthe surface acoustic wave filter, the other ends of the IDTs 2 and 3 areconnected to a ground terminal.

The element chip 30 is housed in a package which can be divided into anupper portion and a lower portion in the bottom-side portion. FIG. 7shows the upper surface of the upper portion 33 of the package bottomportion 31 in which the element chip 30 is mounted, FIG. 8 shows theupper surface of the lower portion 36 of the package bottom portion 31,and FIG. 9 shows the lower surface (bottom surface of the package) ofthe lower portion 36 of the package bottom portion 31.

As shown in FIG. 7, wiring patterns (lands) 42 to 45 are exposed in thedie attachment portion 41 of the upper portion 33 of the package bottomportion 31 and bump-connected to the terminals (pads) of the elementchip 30 by a bump 39, shown by a white circle in FIGS. 6 and 7. In FIG.7, via holes 46 and 47, shown by black circles, pass through the upperportion 33 of the package bottom portion 31 and the wiring patterns 45and 44 and wiring patterns 61 and 63 of the lower portion 36 shown inFIG. 8 are connected. Among external terminals shown in FIG. 9, theright middle external terminal 56 is an unbalanced signal terminal, theleft upper and lower external terminals 52 and 53 are balanced signalterminals, and the other external terminals 54 and 55 are groundterminals. The external terminal 56 defining an unbalanced signalterminal is connected to the unbalanced signal wiring pattern 42 througha castellation 48. The external terminals 52 and 53 defining balancedsignal terminals are connected to the balanced signal wiring patterns 43and 44 through castellations 49 and 50.

Finally, corresponding to the locations of the first and second balancedsignal terminals (pads) 11 and 12 on the element chip 30 shown in FIG.6, as shown in FIG. 7, in the flip-chip mounting package of the elementchip 30, the first balanced signal terminal wiring pattern (pad) 43 isdisposed in the middle of one side of the package, and the secondbalanced signal terminal wiring pattern (land) 44 is disposed in thecorner portion close to the first balanced signal terminal wiringpattern (land) 43. In the element chip 30, a signal line 1 a connectingone end of the IDT 1 and a first balanced signal terminal 11 and asignal line 1 b connecting the other end of the balanced ITD 1 and asecond balanced signal terminal 12 are asymmetrically disposed, andthus, the balancing is deteriorated. Then, as shown in FIG. 9, theexternal terminals 52 and 53 as the first and second balanced signalterminals are disposed so as to be symmetrical around the central axisof the package, and the balancing is adjusted by altering the pathdifference in the package between a signal line connected to theexternal terminal 52 defining the first balanced signal terminal and asignal line connected to the external terminal 53 defining the secondbalanced signal terminal (see, for example, Japanese Unexamined PatentApplication Publication No. 2002-271168).

The surface acoustic wave filter package shown in FIGS. 6 to 9 can bealso used for mounting an element chip 60 including two longitudinallycoupled resonator-type surface acoustic wave filter elements 66 and 68having three IDTs 66 a, 66 b, and 66 c, and 68 a, 68 b, and 68 c and tworeflectors 66 s and 66 t, and 68 s and 68 t, respectively, as shown inFIG. 22. That is, the element chip 30 shown in FIG. 1 and the elementchip 60 shown in FIG. 22 have the same external dimensions and the sameterminal (pad) configuration.

In Japanese Unexamined Patent Application Publication No. 2003-204243, afloat balanced-type surface acoustic wave filter in which the balancingis improved such that two terminals extending on either side in thedirection perpendicular to the surface acoustic wave propagationdirection of the middle ITD of a longitudinally coupled resonator-typesurface acoustic wave filter element are connected to balanced signalterminals, IDTs on both sides are connected to unbalanced signalterminals by using two unbalanced signal lines, and one balanced signalline and one unbalanced signal line intersect in three dimensionsthrough an insulating film is disclosed.

As in the related example shown in FIG. 5, when two elements arecascade-connected and a ground pad is disposed between stages, sincestray capacitance between the wiring for the cascade connection and theground pad is large, there is a problem in that the insertion loss inthe passband is large.

Furthermore, in a surface acoustic wave filter having abalanced-to-unbalanced conversion function which includes balancedsignal terminals that are connected to the terminals on both sides ofone IDT as disclosed in Japanese Unexamined Patent ApplicationPublication No. 2002-271168), since the structure of the package iscomplicated and specific, the configuration of the package is limited tothe element structure.

Accordingly, for example, a surface acoustic wave filter 70 shown inFIG. 10 includes two longitudinally coupled resonator-type filterelements 71 and 72 having three IDTs 71 a, 71 b, and 71 c, and 72 a, 72b, and 72 c and two reflectors 71 s and 71 t, and 72 s and 72 t that arecascade-connected, one end of the middle IDT 71 a of one longitudinallycoupled resonator-type filter element 71 is connected to an unbalancedterminal 73, and one end (one bus bar) of the middle IDT 72 a of theother longitudinally coupled resonator-type filter element 72 is dividedinto two bus bars and the two bus bars are connected to balanced signalterminals 74 and 75.

Another surface acoustic wave filter 80 shown in FIG. 11 includes twosets of surface acoustic wave filter elements 81, 82, 83, and 84 havingthree IDTs 81 a, 81 b, and 81 c; 82 a, 82 b, and 82 c; 83 a, 83 b, and83 c; and 84 a, 84 b, and 84 c and two reflectors 81 s and 81 t; 82 sand 82 t; 83 s and 83 t; and 84 s and 94 t that are cascade-connected,one end of each of the middle IDTs 81 a and 83 a of the surface acousticwave filter elements 81 and 83 is connected to balanced terminals 85 and86, and one end of each of the other surface acoustic wave filterelements 82 and 84 is connected to an unbalanced terminal 87. However,with this configuration, other surface acoustic wave filters cannotshare the package with a surface acoustic wave filter having abalanced-to-unbalanced conversion function of another structuredifferent in terms of the way surface acoustic wave elements arecoupled.

Moreover, since the signal lines inside the package are asymmetrical,the affect of parasitic capacitance, is different between balancedsignal terminals, and, as a result, there is a problem in that thebalancing between balanced signal terminals is deteriorated.

In a surface acoustic wave filter in Japanese Unexamined PatentApplication Publication No. 2002-204243, an intersection is performed byproviding a balanced signal line on a piezoelectric substrate andproviding an unbalanced signal line on an insulating film disposed onthe balanced signal line. Accordingly, the difference between theparasitic capacitance and bridge capacitance entering the two balancedsignal terminals increases and the balancing cannot be sufficientlyimproved.

SUMMARY OF THE INVENTION

To overcome the problems described above, preferred embodiments of thepresent invention provide a surface acoustic wave device including twocascade-connected elements in which insertion loss in the passband isgreatly reduced, and a surface acoustic wave filter which can be housedin a common package with a surface acoustic wave filter having anotherconfiguration, and which has greatly improved balancing between balancedsignal terminals. That is, preferred embodiments of the presentinvention provide a surface acoustic wave device in which thecharacteristics are greatly improved.

A surface acoustic wave device according to a preferred embodiment ofthe present invention includes a substrate, a plurality of terminalsdisposed on the substrate and including at least an unbalanced terminaland two balanced terminals, and at least one surface acoustic waveelement disposed between the unbalanced terminal and the balancedterminals on the substrate. In this surface acoustic wave device,different signal lines connected to the same surface acoustic waveelement intersect through an insulating film.

The substrate may be a piezoelectric substrate in which the entiresubstrate is made of a piezoelectric material or a piezoelectricsubstrate in which a thin film of piezoelectric material (piezoelectricthin film) is disposed on the main body of a substrate made ofnon-piezoelectric material. In the latter case, a piezoelectric thinfilm is provided in at least the portion of a surface acoustic waveelement. A balanced signal is input to or output from a balancedterminal and an unbalanced signal is input to or output from anunbalanced terminal.

When different signal lines connected to the surface acoustic waveelements intersect through an insulating film, the length of the signallines is reduced as compared to when the signal lines are disposed so asnot to intersect, and the restrictions on the locations of the signallines are greatly reduced.

In this manner, for example, when a balanced type surface acoustic wavefilter is constructed by connecting two surface acoustic wave elementsusing signal lines, the insertion loss is reduced such that the lengthsof the signal lines extending between the surface acoustic wave elementsare shortened by reducing the space between the two surface acousticwave elements, and by not providing pads between the surface acousticwave elements.

Furthermore, with the signal lines extending between the surfaceacoustic wave elements and the signal lines extending between thesurface acoustic wave elements and the terminals, since the restrictionson the locations of the lines are reduced, it is easier to provide apackage for common use.

Preferably, the insulating film is polyimide. Since the relativedielectric constant of the polyimide is sufficiently small as comparedto the relative dielectric constant of the piezoelectric substrate,stray capacitance is reduced.

According to a first preferred embodiment, at least two of the surfaceacoustic wave elements are provided. One of the two surface acousticwave elements defines a first element which is connected to theunbalanced terminal and a ground terminal so as to be grounded withdifferent signal lines. The other of the two surface acoustic waveelements defines a second element. At least two signal lines definesignal wirings for connecting the second element and the first element.At least one of the signal wirings and the signal line defining a groundwiring arranged to connect the ground terminal and the first elementintersect through the insulating film. The ground terminal is disposedoutside an area enclosed by the first element, the second element, andthe signal wirings.

In the related device, the ground terminal is disposed inside an areaenclosed by the first element, the second element, and the signalwirings and the insertion loss in the passband is thereby increases.However, according to the above-described configuration, the straycapacitance between the ground terminal and the signal lines isminimized and, as a result, the insertion loss in the passband isgreatly reduced due to the ground terminal being disposed outside anarea enclosed by the first element, the second element, and the signalwirings.

Preferably, the first element includes three IDTs disposed in apropagation direction of a surface acoustic wave, and the unbalancedterminal and the ground terminal are connected to the middle IDT of thethree IDTs. The second element includes three IDTs disposed in thepropagation direction of a surface acoustic wave, and two balancedterminals are connected to the middle IDT of the three IDTs. The IDTs oneither side of the middle IDT of the first element and the IDTs oneither side of the middle IDT of the second element are connected by thesignal wirings.

According to the above configuration, the insertion loss in the passbandof a balanced type SAW filter in which the longitudinally coupledresonator-type SAW filter elements (first element and second element)are cascade connected is greatly reduced.

Preferably, two sets of the first element, the signal wirings, and thesecond element are provided on the substrate. The first element of eachset includes three IDTs disposed in the propagation direction of asurface acoustic wave, and the unbalanced terminal and the groundterminal are connected to the middle IDT of the three IDTS. The secondelement of each set includes one IDT connected to one of the balancedterminals different from that in the other sets. In each set, the twosignal wirings connect the IDTs on either side of the first element andthe IDT of the second element. The first elements of the two sets are inopposite phase to each other.

According to the above configuration, the longitudinally coupledresonator-type SAW filter (first element) connected to a balanced padand the one-port SAW resonator (second element) are connected in series,two sets of these are connected in parallel, the longitudinally coupledresonator-type SAW filter (first element) is arranged to be in oppositephase, and the one-port SAW resonator (second element) is used as atrap. Thus, in a balanced type SAW filter having filter characteristicsimproved, the insertion loss in the passband is greatly reduced.

Preferably, the ground wiring includes a first layer that is notdisposed in the vicinity of the insulating film and a second layer thatis disposed on the vicinity of the insulating film.

According to the above-described structure, regarding the ground wiring,since two layers are disposed one on top of another around theinsulating film, the ground residual impedance is decreased and theattenuation outside the band is improved. Furthermore, the signal wiringmay include only one layer, because two layers are not required to bedisposed one on another around the insulating film, the signal wiring isshortened, and the size is reduced by shortening the distance betweenthe first element and the second element.

According to a second preferred embodiment, at least two surfaceacoustic wave elements are connected to each other. One of the twosurface acoustic wave elements (hereinafter, referred to as a firstsurface acoustic wave element) is a longitudinally coupledresonator-type surface acoustic wave element having three IDTs disposedalong the propagation direction of a surface acoustic wave, and themiddle IDT of the three IDTs is connected to the two balanced signalterminals through the two signal lines (hereinafter, referred to asfirst and second signal lines). The two balanced signal terminals aredisposed on either side of the central axis of the substratesubstantially in parallel to the direction in which the two surfaceacoustic wave elements are arranged. At least one of the first andsecond signal lines is disposed on the insulating film formed on thesubstrate.

In the above-described structure, when at least one of the first andsecond signal lines and the signal line connecting between the surfaceacoustic wave elements intersect, in this intersecting portion, athree-dimensional intersection is provided through an insulating film.

According to the above-described structure, the package can be commonlyused by arranging the balanced signal terminals at the same locations asin a surface acoustic wave filter having another different configurationfor coupling the surface acoustic wave element. Furthermore, regardingthe parasitic capacitance and bridge capacitance entering each of thetwo balanced signal terminals, the difference between them is reduced bydisposing the signal lines connected to the balanced signal terminals onan insulating film and thus, the balancing can be improved.

Preferably, the two balanced signal terminals are disposed so as to besubstantially symmetrical around the central axis of the substrate.

According to the above-described structure, since the balanced signalterminals are disposed substantially in the same location as in asurface acoustic wave filter having another configuration in which thebalanced signal terminals are symmetrically disposed, a common packagecan be used.

Preferably, the second surface acoustic wave element is disposed in thepropagation direction of a surface acoustic wave and is a longitudinallycoupled resonator-type surface acoustic wave filter element having threeIDTs cascade-connected to the first surface acoustic wave element.

According to the above-described structure, the attenuation outside thepassband can be increased.

Preferably, the second surface acoustic wave element is one or aplurality of surface acoustic wave resonator elements connectedtogether.

According to the above-described structure, the attenuation outside thepassband is further increased.

According to a third preferred embodiment, the surface acoustic waveelement is a longitudinally coupled resonator-type surface acoustic wavefilter element including three IDTs disposed along the propagationdirection of a surface acoustic wave, and the middle IDT of the threeIDTs is connected to the two balanced terminals through the signal lines(hereinafter, referred to as first and second signal lines). The twobalanced signal terminals are disposed on both sides of the central axisof the substrate substantially perpendicular to the propagationdirection of a surface acoustic wave. At least one of the first andsecond signal lines is disposed on the insulating film.

In the above-described structure, when at least one of the first andsecond signal lines intersects the signal line and the connection lineconnecting between the IDT and the terminals excluding the balancedterminals, in this intersecting portion, a three-dimensionalintersection is provided through an insulating film.

According to the above-described structure, a common package can be usedby arranging the balanced signal terminals at the same locations as in asurface acoustic wave filter having another configuration in the modefor coupling the surface acoustic wave elements. Furthermore, regardingthe parasitic capacitance and bridge capacitance entering each of thetwo balanced signal terminals, the difference between them is reduced bydisposing the signal lines connected to the balanced signal terminals onan insulating film and thus, the balancing is improved.

In a surface acoustic wave device of the present invention, thecharacteristics are improved. For example, in the first preferredembodiment, the insertion loss in the passband is reduced. Furthermore,in the second and third preferred embodiments, the difference ofparasitic capacitance entering each balanced signal terminal is reducedas compared to the structure described in Japanese Unexamined PatentApplication Publication No. 2002-271168, and the balancing between thebalanced signal terminals is improved. Furthermore, it is possible touse a common package with a surface acoustic wave filter having abalanced-to-unbalanced conversion function with other configurations asshown in FIG. 10, FIG. 11, and accordingly, it is unnecessary to producedifferent packages for exclusive use.

Other features, elements, steps, characteristics and advantages of thepresent invention will become more apparent from the following detaileddescription of preferred embodiments of the present invention withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a balanced type SAW filter according to a firstpreferred embodiment of the present invention.

FIG. 2 is a sectional view taken on line II-II of FIG. 1.

FIG. 3 is a top view of a balanced type SAW filter according to a secondpreferred embodiment of the present invention.

FIG. 4 is a sectional view taken on line IV-IV of FIG. 3.

FIG. 5 is a top view of a balanced type SAW filter according to therelated art.

FIG. 6 shows the structure of a piezoelectric substrate according to therelated art.

FIG. 7 is a top view of the upper portion of a package shown in FIG. 6.

FIG. 8 is a top view of the lower portion of a package shown in FIG. 6.

FIG. 9 shows the bottom surface of a package shown in FIG. 6.

FIG. 10 shows the structure of a surface acoustic wave filter accordingto the related art.

FIG. 11 shows the structure of a surface acoustic wave filter accordingto a reference example.

FIG. 12 shows the structure of a surface acoustic wave filter accordingto a reference example.

FIG. 13 is a top view of a piezoelectric substrate according to a thirdpreferred embodiment of the present invention.

FIG. 14 is a diagram showing characteristics of a surface acoustic wavefilter according to the third preferred embodiment of the presentinvention.

FIG. 15 is a top view of a piezoelectric substrate according to acomparative example.

FIG. 16 is a top view of a piezoelectric substrate according to a fourthpreferred embodiment of the present invention.

FIG. 17 is a top view of a piezoelectric substrate according to a fifthpreferred embodiment of the present invention.

FIG. 18 is a top view of a piezoelectric substrate according to areference example.

FIG. 19 is a top view of a piezoelectric substrate according to anotherreference example.

FIG. 20 is a bottom view of a package according to the third preferredembodiment of the present invention.

FIG. 21 is a top view of a piezoelectric substrate according to a sixthpreferred embodiment of the present invention.

FIG. 22 is a top view of a piezoelectric substrate according to therelated art.

FIG. 23 is a top view of a piezoelectric substrate according to aseventh preferred embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, the preferred embodiments of the present invention aredescribed with reference to FIGS. 1 to 23.

First and second preferred embodiments are described with reference toFIGS. 1 to 4.

First Preferred Embodiment

A surface acoustic wave device according to the first preferredembodiment is described with reference to FIGS. 1 and 2. FIG. 1 is a topview of a substrate 1010 in the surface acoustic wave device of thefirst preferred embodiment, and FIG. 2 is a sectional view taken alongline II-II of FIG. 1.

The surface acoustic wave device according to the first preferredembodiment is preferably an EGSM receiving band filter. For example, theinput impedance is about 50 Ω, the output impedance is about 150 Ω, thepass frequency band is about 925 to about 960 MHz, and the centerfrequency is about 942.5 MHz.

The substrate 1010 is preferably made of a LiTaO₃ single crystalpiezoelectric substrate and a metal film having a fixed pattern isprovided on the main surface 1012 of the substrate 1010 as shown in FIG.2. That is, a balanced-type SAW filter is provided in which alongitudinally coupled resonator-type surface acoustic wave filter 1020(hereinafter, referred to as a filter 1020) of a first stage and alongitudinally coupled resonator-type surface acoustic wave filter 1030(hereinafter, referred to as a filter 1030) of a second stage arecascade-connected, a pad 1051 is an unbalanced terminal, and pads 1052and 1053 are balanced terminals. Signal wirings 1041 and 1042, by whichthe filter 1020 and the filter 1030 are cascade-connected, intersect aground wiring 1048 connected to an IDT 1023 including the unbalancedterminal 1051 in three dimensions. The ground wiring 1048 is connectedto ground pads 1054 and 1055 which are disposed away from the spacebetween the stages. The ground pads 1054 and 1055 are ground terminalsfor grounding. The filters 1020 and 1030 are disposed in parallel suchthat the propagation direction of the surface acoustic waves is parallelto each other.

In the filter 1020 of the first stage, three IDTs 1022, 1023, and 1024are disposed in line with the propagation direction of a surfaceacoustic wave and two reflectors 1021 and 1025 are disposed on eitherside of the IDTs 1022, 1023, and 1024. One electrode side of the middleIDT 1023 is connected to the pad 1051 as an unbalanced terminal througha wiring 1047. The other electrode side is connected to the ground pads1054 and 1055 via the wirings 1040 and 1048 through wirings 1043 and1046. The sides of one electrode of the other IDTs 1022 and 1024 arealso connected to the ground pads 1054 and 1055 through wirings 1044 and1045.

In the filter 1030 of the second stage, three IDTs 1032, 1033, and 1034are disposed in line in the propagation direction of a surface acousticwave and two reflectors 1031 and 1035 are disposed on either side of theIDTs 1032, 1033, and 1034.

One electrode side of the middle IDT 1033 is connected to the pads 1052and 1053 defining balanced terminals and the other electrode is afloating electrode. The sides of one electrode of the IDTs 1032 and 1034disposed on either side of the IDT 1033 are connected to the sides ofthe other electrode of the IDTs 1022 and 1024 of the filter of the firststage. The sides of the other electrode of the IDTs 1032 and 1034 areconnected to the ground pads 1054 and 1055 through wirings 1043 and1046.

Rectangular insulating films 1014 and 1016 are arranged so as to coverportions of the wirings 1041 and 1042 of a signal line connecting thefilters 1020 and 1030, the wiring 1048 is disposed on the insulatingfilms 1014 and 1016, and the wirings 1041 and 1042 and the wiring 1048intersect one another in three dimensions with the insulating films 1014and 1016 disposed therebetween.

In the measurements of the insulating films 1014 and 1016, the dimensionin the transverse direction (in the extending direction of the wiring1048) in the drawing is about 50 μm, the dimension in the longitudinaldirection (in the extending direction of the wirings 1041 and 1042) inthe drawing is about 40 to about 50 μm, and the thickness is about 2 μm.The width of the lower wirings 1041 and 1042 is about 30 μm and thewidth of the upper wiring 1048 is about 20 μm to about 30 μm where thewirings intersect in three dimensions. The space between the filters1020 and 1030 is about 60 to about 70 μm. The dimensions of the groundpads 1054 and 1055 are about 100 μm× about 100 μm. In the relatedexample in which the ground pads having the same dimensions are disposedbetween the two cascade-connected longitudinally coupled resonator-typesurface acoustic wave filters, since the distance between the filters isabout 200 μm, in the first preferred embodiment, the distance betweenthe filter elements is reduced so as to be about one third or less thanthat in the related example. A photosensitive resin (e.g., polyimidehaving a relative dielectric constant of about 2) is preferably used forthe insulating films 1014 and 1016, for example.

In the first preferred embodiment, when the wiring 1048 (also referredto as a ground wiring 1048) for the connection of the ground pads 1054and 1055 and the wirings 1041 and 1042 (also referred to as signalwirings 1041 and 1042) for the connection between the filters 1020 and1030 intersect, the intersecting area seen from the top is sufficientlysmall, the relative dielectric constant of the insulating films 1014 and1016 is sufficiently small as compared to the relative dielectricconstant of the LiTaO₃ substrate 1010 which is about 50, and thethickness of the insulating films 1014 and 1016 is sufficiently large.Accordingly, the stray capacitance is reduced as compared to thestructure in which two elements are cascade-connected and ground padsare disposed between the stages, as in the related example.

Next, the manufacturing method for the substrate 1010 is described.

First, an aluminum film pattern of the first layer is formed on the mainsurface 1012 of the substrate 1010 by dry etching or lift-off, forexample. The aluminum film pattern of the first layer substantiallymatches the final metal pattern of the IDTs, pads and wirings. However,as shown in FIG. 2, regarding the wiring 1048, the pattern of the firstlayer is not formed in the portion where the insulating films 1014 and1016 are formed and in the vicinity thereof such that the insulatinglayers 1014 and 1016 may be disposed between the first layers 1048 a,1048 b, and 1048 c. The thickness of the aluminum film of the firstlayer is approximately the same as the film thickness of the IDTs 1022to 1024 and 1032 to 1034 and, for example, the thickness in an 800 MHzband SAW filter is about 300 nm to about 400 nm and the thickness in a 2GHz band SAW filter is about 150 nm to about 200 nm.

Next, a photosensitive resin is coated and the insulating films 1014 and1016 are formed in the intersecting portion of the wirings 1041 and 1042between the filters 1020 and 1030 and the ground wiring 1048 usingphotolithography, for example.

Next, a resist mask having an opening corresponding to the final metalfilm pattern excluding the exposed portion of the filters 1020 and 1030and the wirings 1041 and 1042 is formed and the aluminum film pattern ofthe second layer is formed using lift-off, for example. Ti or NiCr as anadhesive layer may be formed between the aluminum of the first layer andthe substrate 1010 or between the aluminum of the second layer and thealuminum of the first layer.

In this manner, as shown in FIG. 2, the second layer 1048 s of thewiring 1048 is disposed on top of the first layers 1048 a, 1048 b, and1048 c and connected thereto. In the connection portion between thesecond layer 1048 s and the first layers 1048 a, 1048 b, and 1048 c, theconnection portion must have a fixed area or an area greater than thatrequired to sufficiently reduce the connection resistance between thesecond layer 1048 s and the first layers 1048 a, 1048 b, and 1048 c.Accordingly, in the wiring 1048, the overlapping area between the firstlayers 1048 a, 1048 b, and 1048 c and the second layer 1048 s is atleast about 20 μm per side.

The upper wiring (second layer) of the three-dimensional intersectionmust be connected to the first layer connected to the IDTs at a specificlocation. When the signal line for connecting the two elements isdisposed on the upper side of the three-dimensional intersection, aconnection portion for connecting the first layer and the second layeris required between one of the two elements and the three-dimensionalintersection and between the other of the two elements and thethree-dimensional intersection. That is, the distance between the twoelements must be increased in order to include not only the insulatingfilm of the three-dimensional intersection, but also the connectionportion between the first layer and the second layer.

On the other hand, when the signal lines (wirings 1041 and 1042) forconnecting the two elements (filters 1020 and 1030) are disposed on thelower side of the three-dimensional intersection as in the firstpreferred embodiment, since it is not necessary to provide theconnection portion between the elements and the three-dimensionalintersection, the distance between the two elements is dependent upononly the dimensions of the insulating film of the three-dimensionalintersection.

In particular, in the first preferred embodiment, the middle IDT 1033 inthe second stage is divided and configured to be connected with abalanced output (or balanced input) and no ground wiring is required inthe middle IDT 1033 in the second stage. Accordingly, regarding theground wirings between the filters 1020 and 1030, only the ground wiring1048 for the middle IDT 1023 in the first stage is required.

In the first preferred embodiment, the signal wirings 1041 and 1042between the filters 1020 and 1030 are provided only in the first layerand the electric resistivity of the lines is increased. However, thedistance between the filters 1020 and 1030 is reduced and thedeterioration of the insertion loss in the band is, thus, prevented.

In the surface acoustic wave device of the first preferred embodiment,the stray capacitance between the signal line and the ground pads isreduced by the movement of the ground pads 1054 and 1055 from betweenthe filters 1020 and 1030 and the insertion loss in the passband isdecreased by reducing the between-stage distance (that is, reducing thelength of the signal wirings 1041 and 1042 between the filters 1020 and1030).

Second Preferred Embodiment

Next, a surface acoustic wave device according to a second preferredembodiment of the present invention is described with reference to FIGS.3 and 4. FIG. 3 is a top view of a substrate 1100 in the surfaceacoustic wave device of the second preferred embodiment, and FIG. 4 is asectional view taken on line IV-IV of FIG. 3.

The surface acoustic wave device of the second preferred embodiment is adevice in which the substrate 1100 having a metal film of a fixedpattern disposed on the main surface 1102 is housed in a package (notillustrated), and may be manufactured by the same method as in the firstpreferred embodiment. Hereinafter, the differences between the firstpreferred embodiment and the second preferred embodiment are primarilydescribed.

The surface acoustic wave device of the second preferred embodiment ispreferably a DCS receiving band surface acoustic wave filter. Forexample, the input impedance is about 50 Ω, the output impedance isabout 150 Ω, and the pass frequency band is about 1805 MHz to about 1880MHz.

As shown in FIG. 3, two sets of longitudinally coupled resonator-typeSAW filters 1110 and 1120 (hereinafter, also referred to as filters 1110and 1120) defining first elements are connected in parallel to a pad1173 defining an unbalanced terminal, and pads 1174 and 1175 definebalanced terminals. One-port SAW resonators 1130 and 1140 (hereinafter,referred to as traps 1130 and 1140) defining second elements areconnected in series to the filters 1110 and 1120.

The two-element cascade connection in the longitudinally coupledresonator-type SAW filters as in the first preferred embodiment has theadvantage that high attenuation is achieved outside the passband, but itis at a disadvantage in that the insertion loss in the passband isincreased. As in the second preferred embodiment, high attenuation isachieved in the vicinity of the passband by the series connection of theone-port SAW resonators 1130 and 1140 to the longitudinally coupledresonator-type SAW filters 1110 and 1120. The one-port SAW resonators1130 and 1140 are used as traps where an antiresonant frequency islocated on the higher frequency side of the passband of theresonator-type SAW filters 1110 and 1120.

In the filters 1110 and 1120, three IDTs 1114, 1116, and 1118; and 1124,1126, and 1128 are disposed in line in the propagation direction of asurface acoustic wave, and two reflectors 1112 and 1122 are disposed onboth sides of the IDTs, respectively. One electrode side of the middleIDTs 1116 and 1126 is connected to a pad 1173 defining an unbalancedterminal through wirings 1151 and 1152, respectively. The otherelectrode sides are connected to a ground pad 1172 as a ground terminalthrough wirings 1153 a and 1153, and 1154 a and 1154. One electrode sideof the other IDTs 1114 and 1118, and 1124 and 1128 is also connected tothe ground pad 1172 through wirings 1150 and 1159.

The filter 1110 is opposite in phase to the filter 1120. Furthermore, inthe IDTs 1124 and 1128 of one filter 1120, the intersection is weightedso as to provide adjustment of the balancing.

In the traps 1130 and 1140, reflectors 1132 and 1142 are disposed onboth sides of the IDTs 1134 and 1144. One electrode side of the IDTs1134 and 1144 is connected to the other electrode side of the IDTs 1114and 1118, and 1124 and 1128 of the filters 1110 and 1120 through wirings1155 and 1156, and 1157 and 1158, respectively. The other electrodesides of the IDTs 1134 and 1144 are connected to pads 1174 and 1175defining balanced terminals through wirings 1160 and 1162, respectively.

The wirings 1156 and 1157 intersect the wirings 1153 and 1154 in threedimensions with insulating films 1106 and 1107 disposed therebetween.Furthermore, the wirings 1151 and 1152 also intersect the wiring 1150with the insulating films 1104 and 1105 disposed therebetween.

As for the dimensions of the insulating films 1104, 1105, 1106, and1107, the dimension in the transverse direction (extending direction ofthe wirings 1150, 1153, and 1154) in FIG. 3 is about 70 μm, thedimension in the longitudinal direction (extending direction of thewirings 1151 and 1152 and perpendicular to the extending direction ofthe wirings 1153 and 1154) in FIG. 3 is about 40 to about 50 μm, and thethickness is about 2 μm. The width of the lower wirings 1150, 1156, and1157 in the three dimensional intersection is about 30 μm and the widthof the upper wirings 1151, 1152, 1153, and 1154 is about 20 μm to about30 μm. The space between the filters 1110 and 1120 and the traps 1130and 1140 is about 60 μm to about 70 μm. The dimensions of the ground pad1172 are about 100 μm× about 100 μm. In the related example where theground pad of the same dimensions is disposed between the filter and thetrap, the space between the filter and the trap is about 200 μm, and, inthe second preferred embodiment, the space between the filters 1110 and1120 and the traps 1130 and 1140 is about one third or less than that inthe related example.

As shown in FIG. 4, second layers 1153 s and 1154 s of the wirings 1153and 1154 are disposed on the insulating layers 1106 and 1107, and thesecond layers 1153 s and 1154 s are disposed on the first layer 1172 aof the ground pad 1172 and wirings 1153 a and 1154 a of only the firstlayer on the both sides of the insulating films 1106 and 1107. The firstlayer is disposed on the second layer in an area of at least about 20 μmper side and both are connected.

Moreover, the second layer is formed in the pads 1172, 1173; 1174, and1175, the middle portion of the wiring 1150, and the wirings 1151, 1152,1153, 1154, 1159, 1160, and 1162.

In the second preferred embodiment, the three dimensional wiring isprovided between the filters 1110 and 1120 and the traps 1130 and 1140,but the same effect as in the first preferred embodiment may beobtained. That is, since the space between the two elements of thefilters 1110 and 1120 and the traps 1130 and 1140 can be determined byonly the dimensions of the insulating films 1106 and 1107 for threedimensional intersection, the space is relatively small.

Since no ground wiring is required in the traps 1130 and 1140, only oneground wiring is required between the two elements for grounding thefilters 1110 and 1120. Even if the wirings 1155 and 1156, and 1157 and1158 between the two elements are provided by only the first layer andthe electric resistivity of the lines increases, since the distancebetween the two elements is reduced, the deterioration of the insertionloss in the band is prevented.

Next, third to seventh preferred embodiments are described withreference to FIGS. 12 to 21 and FIG. 23. Moreover, in the drawings, thesame reference numerals are given to the same structure elements asdescribed above.

Third Preferred Embodiment

A surface acoustic wave filter according to a third preferred embodimentis described with reference to FIGS. 12 to 19 and FIG. 22. The surfaceacoustic wave filter of the third preferred embodiment includes abalanced-to-unbalanced conversion function. Here, an EGSM (extendedglobal system for mobile communications) receiving filter in which theimpedance of an unbalanced signal terminal is about 50 Ω and theimpedance of a balanced signal terminal is about 100 Ω is described asan example.

First, the structure of the third preferred embodiment is described withreference to FIGS. 12 and 13.

In the surface acoustic wave filter of the third preferred embodiment,two longitudinally coupled resonator-type surface acoustic wave filterelements (hereinafter, referred to as filter elements) 101 and 102 areprovided on a piezoelectric substrate 100 and cascade connected. ALiTaO₃ 40 ±5° Y-cut X-propagation substrate is preferably used as thepiezoelectric substrate 100 and the filter elements 101 and 102 aredefined by aluminum electrodes.

As shown in FIG. 12, one filter element 101 includes three IDTs 103,104, and 105 and two reflectors 106 and 107 disposed along thepropagation direction of a surface acoustic wave. The IDTs 103 and 105are disposed so as to sandwich the middle IDT 104 and the reflectors 106and 107 are disposed on both sides of the IDTs 103 and 105. One end ofthe middle IDT 104 is connected to an unbalanced signal terminal 117 bya signal line 122.

In the same manner, the other filter element 102 also includes threeIDTs 108, 109, and 110 and two reflectors 111 and 112 disposed along thepropagation direction of a surface acoustic wave. The IDTs 108 and 110are disposed so as to sandwich the middle IDT 109 and the reflectors 111and 112 are disposed on both sides of the IDTs 108 and 110. Both ends ofthe middle IDT 109 are connected to balanced signal terminals 118 and119 by signal lines 123 and 124, respectively.

The two filter elements 101 and 102 are cascade connected. That is, oneend of the IDTs 103 and 105 of the filter element 101 is connected toone end of the IDTs 108 and 110 of the other element 102 via signallines 120 and 121, respectively. The other end of the IDTs 103 and 105of the filter element 101 and the other end of the IDTs 108 and 110 ofthe other filter element 102 are grounded, respectively. Moreover, evenif the other ends are connected to each other in the same manner as theone ends, instead of being connected to the ground, there is no problemin the operation of the surface acoustic wave filter.

The direction of each of the IDTs 103, 104, 105, 108, 109, and 110 isadjusted such that the phase of an electric signal transmitted on asignal line 120 connected between the IDTs 103 and 108 is approximately180 degrees different from the phase of an electric signal transmittedon a signal line 121 connected between the IDTs 105 and 110. Thus,excellent amplitude balancing and phase balancing of the surfaceacoustic wave filter is obtained.

In the portions shown by reference numerals 113 to 116 (hereinafter,referred to as narrow-pitched electrode finger portions) in FIG. 12,that is, in the portions between the IDTs 103 and 104 and between theIDTs 104 and 105 of the filter element 101 and between the IDTs 108 and109 and between the IDTs 109 and 110 of the filter element 102, thepitch of a few adjacent electrode fingers (width of an electrode fingerand space between electrode fingers) is less than that in the otherportion of the IDTs 103, 104, 105, 108, 109, and 110. Moreover, in FIG.12, for simplicity, the number of electrode fingers is illustrated so asto be less than the actual number of electrode fingers. A broad bandpassfilter is obtained by reducing the discontinuity at the portions whereIDTs that are adjacent to each other to the maximum extent by includingsuch narrow-pitched electrode finger portions 113 to 116, and byadjusting the space between the IDTs 103, 104, 105, 108, 109, and 110.

FIG. 13 shows the actual layout on a piezoelectric substrate 100. InFIG. 13, the oblique line portion having a narrow space is an electrodepattern (hereinafter, referred to as a first layer pattern) formed usinga first photolithographic process, for example. The oblique line portionhaving a wide space is an electrode pattern (hereinafter, referred to asa second layer pattern) formed using a second photolithographic process,for example. The portions having no oblique line 250, 251, and 252 areinsulating films formed using a resin having a low dielectric constantbefore the second layer pattern is formed. In FIG. 13, for brevity, thefirst layer pattern and the second layer pattern are illustrated so asto be in contact with each other, but actually, at least one of thefirst layer pattern and the second layer pattern is formed so as to belarger than the illustration in the vicinity of the location where bothare in contact with each other and the second layer pattern is disposedon the first layer pattern to connect both.

The unbalanced terminal 117 is disposed in the upper middle portion ofthe piezoelectric substrate 100 in FIG. 13. The balanced signalterminals 118 and 119 are disposed in the lower left and right portionsof the piezoelectric substrate 100 in FIG. 13, respectively. Groundterminals 201 and 202 are disposed in the upper left and right portionsof the piezoelectric substrate 100 in FIG. 13, respectively. That is,the balanced signal terminals 118 and 119 are arranged so as to besymmetrical about an imaginary central axis of the piezoelectricsubstrate 100.

One terminal of the middle IDT 104 of one filter element 101 isconnected to the unbalanced terminal 117 and the other terminal isconnected to the ground terminal 202. One end of the IDTs 103 and 105 onboth sides of one filter element 101 is connected to the groundterminals 201 and 202, respectively, and the other end is connected toone end of the IDTs 108 and 110 of the other filter element 102 throughthe signal lines 120 and 121, respectively. The connection line forconnecting the other end of the middle IDT 104 to the ground terminal202 intersects the signal line 201 in three dimensions through aninsulating film 251 disposed on the signal line 121 for connectingbetween the IDTs 105 and 110 in the portion shown by reference numeral203.

The other end of the IDT 108 of the filter element 102 is connected tothe ground terminal 201 through the reflectors 111 and 106. That is, theother end of the IDT 108 and the reflector 111 are connected by aconnection line 130, the reflectors 106 and 110 are connected by aconnection line 131, and the reflector 106 and the ground terminal 201are connected. The other end of the IDT 110 is connected to the groundterminal 202. One end of the middle IDT 109 is connected to one balancedsignal terminal 118 by a signal line 123. The majority of the signalline 123 is disposed on an insulating film 250. The signal line 123intersects the connection line for connecting the reflectors 106 and 111in three dimensions through the insulating film 250 in the portion shownby reference numeral 204 and intersects the signal line 120 forconnecting between the IDTs 103 and 108 in three dimensions through theinsulating film 250 in the portion shown by reference numeral 205. Theother end of the IDT 109 is connected to the other balanced signalterminal 119 by a signal line 124. An insulating film 252 is disposedbetween the signal line 124 and the substrate 100 and the symmetrybetween the balanced signal terminals is maintained.

Next, the method for forming each pattern on the substrate 100 isdescribed.

First, an aluminum film pattern of a first layer is formed on thesubstrate 100 by a dry etching method or a lift-off method, for example.The aluminum film pattern of the first layer includes the IDTs 103, 104,and 105; 108, 109, and 110, the reflectors 106 and 107; and 111 and 112,the signal lines 120 and 121, and the connection lines 130 and 131. Thethickness of the aluminum film of the first layer is substantially thesame in the IDTs 103, 104, and 105; and 108, 109, and 110.

Next, a photosensitive resin is coated on the substrate 100 and theinsulating films 250, 251, and 252 are formed using a photolithographymethod, for example. Polyimide (relative dielectric constant: 2) is usedas a photosensitive resin, for example. In this case, since the relativedielectric constant is sufficiently small as compared to the relativedielectric constant of about 50 of the LiTaO₃ substrate 100, when thesignal lines 123 and 124 connected to the balanced signal terminals 118and 119 are formed on the insulating films 250 and 251, the straycapacitance is reduced as compared to the case in which a signal lineconnected to a balanced signal terminal is formed directly on asubstrate.

Next, a resist mask having an opening corresponding to the second layerpattern is formed on the substrate 100 and an aluminum film pattern ofthe second layer is formed using a lift-off method, for example.

Moreover, an adhesive layer of, for example, Ti or NiCr may be formedbetween the aluminum film of the first layer and the substrate 100 orbetween the aluminum film of the second layer and the aluminum film ofthe first layer.

In FIG. 20, the layout of external terminals 401 to 405 on the bottomsurface of a package for the surface acoustic wave filter of the thirdpreferred embodiment is shown. In FIG. 20, the upper middle externalterminal 401 is an unbalanced terminal and is connected to the terminal117 shown in FIGS. 12 and 13. The external terminals 402 and 403 in thelower right and lower left corner portions are balanced signal terminalsand are connected to the terminals 118 and 119 shown in FIGS. 12 and 13,respectively. The external terminals 404 and 405 in the middle portionsare ground terminals.

FIGS. 18 and 19 shown surface acoustic wave filter element chips havinga balanced-to-unbalanced conversion function with various otherconfigurations in which surface acoustic wave elements 71 and 72, and 81to 84 are provided on piezoelectric substrates 70 and 80, which aresubstantially the same size as the piezoelectric substrate 100 so as tobe housed in a common package. FIG. 18 corresponds to the structureshown in FIG. 10 and FIG. 19 corresponds to the structure shown in FIG.11. In the surface acoustic wave filters having a balanced to unbalancedconversion function with the other configurations, in the same manner asthe piezoelectric substrate 100 of the third preferred embodiment,unbalanced terminals 73 and 87 are disposed in the upper middle portionof the piezoelectric substrates 70 and 80, balanced signal terminals 74and 75, and 86 and 85 are disposed in the lower left and right portions,and the ground terminals 76 and 77, 88 and 89 are disposed in the upperleft and right portions.

Accordingly, the surface acoustic wave filter of the third preferredembodiment and the surface acoustic wave filters having abalanced-to-unbalanced conversion function with the other configurationsas shown in FIGS. 18 and 19 can be housed in a common package.

Moreover, in FIGS. 18 and 19, the first layer pattern, the second layerpattern, and the insulating film pattern are illustrated in the samemanner as in FIG. 13. In FIG. 18, the signal lines between the IDTs 71 band 72 b and between the IDTs 71 c and 72 c and the connection line forconnecting between the IDT 71 a and the second terminals 76 and 77intersect in three dimensions through insulating films 78 and 79. InFIG. 19, the signal lines for connecting between the IDTs 84 a and 82 aand the terminal 87 and the connection lines for connecting between theIDTs 84 b and 82 c and the terminals 88 and 89 intersect in threedimensions through insulating films 90 and 91, and the signal lines forconnecting between the IDTs 83 a and 81 a and the terminals 86 and 85and the connection lines for connecting between the IDTs 83 b and 81 cand the terminals 88 and 89 intersect in three dimensions throughinsulating films 92 and 93.

Next, one example of the design of the surface acoustic wave filterelements 101 and 102 is provided. When the wavelength determined by thepitch of the electrode fingers where the pitch is not narrowed except innarrow-pitched electrode finger portions 113 to 116 is represented byλ_(I), the following relationship is obtained.

-   Cross width: 48.1 λ_(I)-   Number of electrode fingers of filter element 101 (in the order of    IDTs 103, 104, and 105): 28(6)/(6)24(6)/(6)28 (number of    narrow-pitched electrode fingers represented by the number in the    parentheses)-   Number of electrode fingers of filter element 102 (in the order of    IDTs 108, 109, and 110): 28(6)/(3)24(3)/(6) 28 (number of    narrow-pitched electrode fingers represented by the number in the    parentheses)-   Number of reflectors: 80-   Metallization ratio: 0.70-   Electrode film thickness: 0.080 λ_(I)

FIG. 14 shows the relationship between the frequency and common-modeattenuation characteristics of the above-described design example (thirdpreferred embodiment). The common-mode attenuation characteristics showthe balancing between balanced signal terminals, and that as theattenuation increases, the balancing between balanced signal terminalsimproves.

In FIG. 14, as a comparative example, the relationship between thefrequency and common-mode attenuation characteristics where an extrawiring for balanced signal terminals is included inside a package as inJapanese Unexamined Patent Application Publication No. 2002-271168 andthe layout of the terminals on the bottom surface of the package is thesame as that shown in FIG. 20. The layout on the piezoelectric substrateof the comparative example is shown in FIG. 15. The specification of thefilter elements 101 and 102 is the same as that of the above designexample (third preferred embodiment). FIG. 15 shows the layout on apiezoelectric substrate 300 in which an unbalanced signal terminal 117′is disposed in the upper middle portion, a balanced signal terminal 118′is disposed on the slightly right side from the middle, and a balancedsignal terminal 119′ is disposed on the lower right portion. A groundterminal 301 is disposed in the upper left portion, a ground terminal302 is disposed in the upper right portion, a ground terminal 303 isdisposed on the slightly left side from the middle, and a groundterminal 304 is disposed in the lower left portion.

The passband of the EGSM receiving filter is about 925 MHz to about 960MHz. In FIG. 14, when the greatest common-mode attenuation is comparedin the frequency band, although the common-mode attenuation is about24.0 dB in the comparative example, the common mode attenuation is about27.5 dB in the preferred embodiment and, as a result, the common modeattenuation improves by about 3.5 dB as compared to the comparativeexample.

One of the main causes of this effect is that, since the asymmetricalextra wiring connected to the balanced signal terminals in thecomparative example is not provided in the preferred embodiment, thedifference of the effect of parasitic capacitance is eliminated, and,since, in the preferred embodiment, the signal lines 123 and 124 forconnecting between the IDTs and the balanced signal terminals on thepiezoelectric substrate are provided on an insulating film pattern madeof a resin having a low dielectric constant, even if the lengths of thesignal lines 123 and 124 are different from each other on thepiezoelectric substrate, the difference of the parasitic capacitanceentering each balanced terminal is minimal.

As described above, according to the third preferred embodiment, whenthe terminals of the middle IDT in the three IDTs in a longitudinallycoupled resonator-type surface acoustic wave filter having three IDTsare connected to balanced signal terminals, a filter having an greatlyimproved balancing between the balanced signal terminals is obtained.Furthermore, the above-described surface acoustic wave filter and asurface acoustic wave filter having a balanced to unbalanced conversionfunction of another configuration can be housed in a common package.

Next, fourth to seventh preferred embodiments are described. The fourthto seventh preferred embodiments achieve the same effects as thoseachieved in the third preferred embodiment. Hereinafter, the differencesbetween the fourth to seventh preferred embodiments and the thirdpreferred embodiment are primarily described.

Fourth Preferred Embodiment

The signal lines 123 and 124 are disposed on the insulating films 250and 251 in the third preferred embodiment. However, in the fourthpreferred embodiment, as shown in FIG. 16, only the longer signal line123 is disposed on the insulating film 250.

Fifth Preferred Embodiment

As shown in FIG. 17, the connecting method between the IDT 108 and theground terminal is different from that in the third preferredembodiment. That is, there is no connecting line for connecting betweenthe IDT 108 and the reflector 111, between the reflectors 106 and 111,and between the reflector 106 and the ground terminal 201. Instead, forconnecting to the ground terminal 202, a connection line 132 forconnecting to the IDT 108 is defined by the first layer pattern. Theconnection line 132 is connected to a connection line of the secondlayer pattern for connecting between the IDT 110 and the ground terminal202. The insulating film 252 is provided on the connection line 132 andintersects the signal line 124 for connecting between the middle IDT 109and a balanced signal terminal 119 in three dimensions.

Sixth Preferred Embodiment

As shown in FIG. 21, a surface acoustic wave resonator element(hereinafter, referred to as a resonator element) 150 is connected inseries to the filter element 102. Also in this case, the attenuationoutside the passband is increased in the same manner as in the third tofifth preferred embodiments in which the two longitudinally coupledresonator-type surface acoustic wave filter elements are cascadeconnected.

In the resonator element 150, reflectors 152 and 153 are disposed onboth sides of an IDT 151. One end of the IDT 151 is connected to anunbalanced signal terminal 117 and the other end is connected to oneends of the IDTs 108 and 110 of the filter element 102 by signal lines120′ and 121′.

The pattern of the first layer includes the filter element 102, theresonator element 150, the signal lines 120′ and 121′, the connectionline 130 between the IDT and the reflector 111, and a connection line131′ extending from the reflector 111 to the middle on the side of theresonator element 150. The connection line 131′ extending to the middleon the side of the resonator element 150 is connected to the groundterminal 201 by the connection line of the second layer pattern. Thesignal line 123 for connecting between the IDT 109 of the filter element102 and the balanced terminal 118 intersects the signal line 120′ andthe connection line 131′ in three dimensions through the insulating film250.

In the resonator element 150, one end of the IDT 151 is connected to theground terminal 201 or 202, the other end connected to the filter 102 isconnected to the unbalanced terminal 117 by the signal lines 120′ and121′, and the resonator element 105 may be connected in parallel to thefilter element 102.

Furthermore, in the resonator 150, a plurality of resonator elements maybe connected in series or in parallel.

Seventh Preferred Embodiment

As shown in FIG. 23, only one filter element 502 is disposed on apiezoelectric substrate 500. Also in this case, a filter having greatlyimproved balancing between balanced signal terminals 518 and 519 isobtained in the same manner as in the third through sixth preferredembodiments. Furthermore, the filter and a surface acoustic wave filterhaving a balanced to unbalanced conversion function of anotherconfiguration can be housed in a common package.

The filter element 502 includes reflectors 511 and 512 on both sides ofthree IDTs 508, 509, and 510. One end of the IDT 508 is connected to asignal line 520′ and one end of the IDT 510 is connected to a signalline 521′. The signal lines 520′ and 521′ are connected to an unbalancedterminal 517 by a connection line of the second layer pattern.

The pattern of the first layer includes the filter element 502, thesignal lines 520′ and 521′, and a connection line 530 for connectingbetween the other end of the IDT 508 and the reflector 511. A connectionline 531′ extending to the middle from the reflector 511 is connected toa ground terminal 601 by the connection line of the second layerpattern. The other end of the IDT 510 is connected to a ground terminal602 by the connection line of the second layer pattern. A signal line523 for connecting between one end of the IDT 509 of the filter element502 and one balanced terminal 518 intersects the signal line 520′ andthe connection line 531′ in three dimensions through an insulating film650. An insulating film 652 is also provided between a signal line 524for connecting between the other end of the IDT 509 of the filterelement 502 and the other balanced terminal 519 and the piezoelectricsubstrate 500.

As described above, in the surface acoustic wave filter of the third toseventh preferred embodiments, since the layout of each terminal (bump)disposed on the piezoelectric substrate can be made substantially thesame as each terminal (bump) in the element chip of a surface acousticwave filter of another configuration, the above-described surfaceacoustic wave filter and the surface acoustic wave filter of anotherconfiguration can be housed in a common package.

Furthermore, since the differences in the routes between signal lines inan element chip are substantially reduced by providing signal linesconnected to balanced signal terminals on an insulating film patternprovided on a piezoelectric substrate, balancing is greatly improvedwithout providing the different routes in a package.

According to the first to seventh preferred embodiments, characteristicsof a surface acoustic wave device are greatly improved.

Moreover, the present invention is not limited to the above-describedpreferred embodiments, and various modifications can be made.

For example, other than LiTaO₃, a single crystal substrate of quartz,LiNbO₃, or other suitable material can be used as a substrate.Furthermore, the present invention can be applied to a surface acousticwave device using a piezoelectric thin film of ZnO, AlN, or othersuitable piezoelectric thin film.

For example, although a 40±5° Y-cut X-propagation LiTaO₃ substrate isused in the third to seventh preferred embodiments, in the presentinvention, the substrate is not limited thereto, and the same effect canbe obtained by using a substrate of 64 to 72° Y-cut X-propagationLiNbO₃, 41° Y-cut X-propagation LiNbO₃, or other suitable substrate.

Furthermore, the present invention can be applied to not only a surfaceacoustic wave filter having a balanced-to-unbalanced conversionfunction, but also to a surface acoustic wave filter having abalanced-to-balanced conversion function.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing the scope andspirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

1. A surface acoustic wave device comprising: a substrate; a pluralityof terminals disposed on the substrate and including at least anunbalanced terminal and two balanced terminals; at least two surfaceacoustic wave elements disposed on the substrate between the unbalancedterminal and the balanced terminals; and a plurality of signal linesconnected to the at least two surface acoustic wave elements; wherein atleast two of the plurality of signal lines connected to the at least twosurface acoustic wave elements intersect one another with an insulatingfilm disposed therebetween; one of the at least two surface acousticwave elements defines a first element that is connected to theunbalanced terminal and to a ground pad; another of the at least twosurface acoustic wave elements defines a second element; at least two ofthe plurality of signal lines define signal wirings arranged to connectthe second element to the first element; at least one of the pluralityof signal lines defines a ground wiring arranged to connect the firstelement to the ground pad; at least one of the signal wirings and theground wiring intersect with the insulating film disposed therebetween;the ground pad is disposed outside of an area enclosed by the firstelement, the second element and the signal wirings; and the groundwiring includes a first layer which is not disposed in the vicinity ofthe insulating film and a second layer which is disposed in the vicinityof the insulating film.
 2. The surface acoustic wave device as claimedin claim 1, wherein the insulating film is polyimide.
 3. The surfaceacoustic wave device as claimed in claim 1, wherein the first elementincludes three IDTs disposed in a propagation direction of a surfaceacoustic wave, and the unbalanced terminal and the ground pad areconnected to a middle IDT of the three IDTs; the second element includesthree IDTs arranged in the propagation direction of the surface acousticwave, and the two balanced terminals are connected to a middle IDT ofthe three IDTs; and the IDTs on either side of the middle IDT of thefirst element and the IDTs on either side of the middle IDT of thesecond element are connected by the signal wirings.
 4. The surfaceacoustic wave device as claimed in claim 1, wherein two sets of thefirst element, the signal wirings, and the second element are providedon the substrate; the first element of each set includes three IDTsdisposed in a propagation direction of a surface acoustic wave, and theunbalanced terminal and the ground pad are connected to a middle IDT ofthe three IDTs; the second element of each set includes one IDTconnected to one of the balanced terminals that is different from thatin the other set; in each set, the two signal wirings connect the IDTson either side of the middle IDT of the first element and the IDT of thesecond element; and the first elements of the two sets are opposite inphase with respect to each other.
 5. The surface acoustic wave device asclaimed in claim 1, wherein the at least two surface acoustic waveelements are connected to each other; the first element is alongitudinally coupled resonator-type surface acoustic wave elementhaving three IDTs disposed along a propagation direction of a surfaceacoustic wave, and the middle IDT of the three IDTs is connected to thetwo balanced signal terminals through first and second signal lines ofthe plurality of signal lines; the two balanced signal terminals aredisposed on either side of a central axis of the substrate substantiallyin parallel to the direction in which the at least two surface acousticwave elements are arranged; and at least one of the first and secondsignal lines is disposed on the insulating film.
 6. The surface acousticwave device as claimed in claim 5, wherein the two balanced signalterminals are disposed so as to be substantially symmetrical about thecentral axis of the substrate.
 7. The surface acoustic wave device asclaimed in claim 5, wherein the second surface acoustic wave element isdisposed in the propagation direction of a surface acoustic wave and isa longitudinally coupled resonator-type surface acoustic wave filterelement having three IDTs cascade-connected connected to the firstsurface acoustic wave element.
 8. The surface acoustic wave device asclaimed in claim 5, wherein the second element includes one surfaceacoustic wave resonator element.
 9. The surface acoustic wave device asclaimed in claim 5, wherein the second element includes a plurality ofsurface acoustic wave resonator elements connected together.
 10. Thesurface acoustic wave device as claimed in claim 1, wherein one of theat least two surface acoustic wave element is a longitudinally coupledresonator-type surface acoustic wave filter element including three IDTsdisposed along a propagation direction of a surface acoustic wave, and amiddle IDT of the three IDTs is connected to the two balanced terminalsthrough first and second signal lines of the plurality of signal lines;the balanced signal terminals are disposed on both sides of a centralaxis of the substrate substantially perpendicular to the propagationdirection of a surface acoustic wave; and at least one of the first andsecond signal lines is disposed on the insulating film.
 11. The surfaceacoustic wave device as claimed in claim 1, wherein the substrate is aLiTaO₃ single crystal piezoelectric substrate.
 12. The surface acousticwave device as claimed in claim 1, wherein the substrate is a LiTaO₃40±5° Y-cut X-propagation substrate.
 13. The surface acoustic wavedevice as claimed in claim 1, wherein the first and second layers of theground wiring are made of Al.
 14. The surface acoustic wave device asclaimed in claim 13, wherein an adhesive layer is disposed between thefirst and second layers of the ground wiring.
 15. The surface acousticwave device as claimed in claim 14, wherein the adhesive layer is madeof one of Ti and NiCr.